Process for the treatment of raw materials containing silicic acid or silicates and oxides of heavy or light metals



, Patented Aug. 2, 1.933"

- UNITED FSTTES Y' PRocE'ss "Fon THE 'rrtmrmnroraw MATERIALS VCONTAINING SILICIC .ACID

Y `on srLxcATEs AND lJustus Kohlmeyer and lXaver fSiiebersi'. iBerlin-Charlottenburgy Germany? .4

No. Drawing.l appliation Dcemberjfie, 1930,- 'i

.sei-isi No.. 502,856,

Th oxides f" thev igit metaisand nigh melting heavy metals (aluminium, beryllium,vmagne sium,y zirconium, chromium; vanadium andthe lil'ieyareA found yin nature forthe greater partin the form o f compounds with'silici'c acid or with silicio acid as gangue. M 'Y The hitherto known processes for the removal of the 'silicio acid by sintering or melting with additions, by nxiviation or theiike di@ not, however, givethe'possibility of removingthe' very'firrI-jA portant quantities of 'silicio acid `from the' said oxide raw materialsI in sufcient quantity. TheA production, of alumina from silicc acid-rich'ma-g terial' is the basis of the following process.` `The .Y

hitherto patented processes for the production 'of alumina consisted of sinteringwith sodaor alkali in rotary ovens invorder 'to convert the alumina into water-soluble compounds and Vto se'pairate'` the associated materiails` as insoluble products. Since, however,f,the silicio cidv also 4gives water solublecompounds with alkalies' the raw mate-ff rial mustonlycontain small percentages oi' silicio acid, so 1that the sources :of supply ofthe raw '25 1n order to avoid'this disadvantage a process was invented according to which theraw materialwas materials suitable for use would'lbe 'very limtedf vheatedfwithV metal sulphides y `whose ,sulphur for example in the caseV of'a1uminaproduct i on was` lirikdtfjl the alumina with the'iformationV of aluminium sulphide in order rto takeup;` in liquid. condition, the reduced siliconV inthe form-of alloy; For example, alumina'contai'ning silica is K5heated with. iron' sulphide and.additionL of carbon'toprodu'cev aluminium sulphideV and "ferroesilico'i. Since thi's'i'reaction can onlytalge place liquid form't is possible that',o n. account ovi4 equilibe. rum arising,l the conversion'.does,not` proceed to completion and the twoelementsF `and"Si fare present. in variousiorrns diifer'ent fusion prodi' uctsj such asAizo-fAizsg melt, iron sulphide..mein.l

and nally a metallic melt,'sothat separation and treatment of Aindividual phases must 'be effected by separate processes' v f. .-2

In a similar classj lies a process furthe production of metals from sulphide ores. VThis process consists in obtaining metals from heayy'met'al sulphidic ores, diflicultly reducexab'le oxides being added in order, either to remove the dissociated sulphide sulphur, or in part, in .thereduced form, to ract as desulphidizing agents forthefsulphidier oresand to form analloy with the heavy'metals such; for example as Fe andS'i. Theobject .ofV the present-application, namely .alcomplete ref moval of l theY siliconk jfrom ther-original foxides' `is greatlyV dierentiated from thisrknownprocessj the v'apourizatiori asV SiS is utilized.

and Germany vApril .-9,

v 21 claims. "'(Cl. .2 3-{132) v where ltige'siiica kisreduceiijand converted into anr alloy'. This results"- directly 'from 'a manner" of .operationfwith this'known process which does not v provnie a wholly liornogeneouscharge consisting'A of a single'mixture but of: a charge of' oxide'bri-- quette's plus sulphidev ores. fvThe'' diiiicultlyre- `ducab1e-joxids--.are jnrstredud 'to metals, `metalloid's orcarbides: which then, act to .desulu .1000 'and 150`0` Cfare recapitulated and an indication o`fL given inc sulphide .the mais characteristics @flee mess,

commences?. to "v yap'ouriuzel in l inert-r atmospheres at 1'1070o C. and. givesayery high timate 'adn'iture with carborif the yapourization temperature' is reduced by. `100 tojl 150 CL which.. isr attributable'A tothe "formation of a more easily yapourviza'ble Vzizifc-canbfon-sulr'iliurcompound. Ai corresponding `Zinc'.-- s ilico'n-sulphur compound is,`l

howeyer, very appreciably more easily vapouriz 'able a'sshownfi'n that a".rxjdxture of. zinc blend Z'nS` with silicon lin st'oicometric. proportions' l.: 1r com,- mences to Vapourize ,alre'adyfat'abiitQOUJCQ and` at 'abgut 1270o cg'attains 'a veryjiii'ghdgree of .Vapourixzaftionl .Thef.forination' this.partic-` uiafriyg L,easily f vapourizabie .zinc'f-smcons'ipiir compound forms `the basis of the present f aDl51i".

` "cation: j It "can Lbefin'thvis 'case leftopen as .to

'whether 'atrue Zn-Si-S compoundis formed'or iiportntthmg isfthjap Ai1; Lis silicon*sublsiiiiiinde SiS whiclicomes in'qestion and'not siliconfdi- :y I i sulphide SiSz. 'Ifhisfollowseyen Von thegro'und that'in'.theyapurizationzofsiliconas SiSfdou.-

ble--theduantity of sulphurfis" necessary a's when i l`By thefinvestig'ation of thevpresent has been' found that Vvthe. above described" zinc- `carbonesulphurfcoinpound"is a' verypowerful reducing agent fory silicicac'id'; Thequarts lvess/el f process it v in which the vapourization of zinc-carbon-sul Vio phur wascarried out was strongly corroded. The

silicon which was reduced out either takes theplace of carbonin the Zn-C-S compound or, as

. mentioned above, forms when heated Zn-i- SisLm It must also be expected that when silicio acid,

zinc sulphide and carbonare mixed together with one another the reductionof the SiOzby Zn- C-SVA in the nascent state takes place even more ener-v getically as lwas shown .by investigation. This action began at a temperature 'of about 1000 C.

' while'at '140.0o C. conversion at the Sametimek was tothe extent of 99%. 'f

It must Vnow be shown as tothe behaviour of A1203 when heated in association with zinc' suli plaide. Alumina alone is not sulphidized by ZnS inV inert atmospherea It is, however, in'admixture with carbon. I n therst place similar conl ditions arise as in the reaction of S102 with zincY sulphide and carbon, i.. e. the formation of gasf ecus Zn-C-S results which'thenreacts to reduce the alumina. Animportant point in thisk is that v in `contradistinction''to the reactionfwith silicio upwards'andiurther that, `in contradistinctlon to vsilicon sulphide, aluminium sulphidefis not g, mentioned the formation of SiS; as a cons equeric'e 165 of. the possible' reaction between-Al2Oa Yand 4SiOv acid,^the' Vreaction with` alumina'joccurs at ap'- preciablvhigher temperatures of `from 14.50 C.

volatile jorviaonly, volatile at very high temperatures andthenonly to a limited extent.

Further investigation has shownrthatalumin-'I ium sulphide AlzSs which Vdoes not react with metallic silicon'does"sof-with silicicacid and is converted into volatile silicon sulphide.

2A12s3+3sio2;=2A12o3+3sis2 f l The essentialthing in this reaction is, how*- ever, Athatfin part in consequence of the forma'- tion of vAl-Ssorlly occurring at high temperature,

. the reaction does not occur until these high temperatures areattained 'and further at these high temperatures the reaction-with'AlzSs resultsifin the formation ofsilicon disulphide SiSz and not quantity of SiS onlya half rof the molecular equivalent of `'SiSffis vapourized'. Ofparticular im'- portancefis the i'actj that as alreadystated this latter reaction occurs only `at' raisedv temperature." `vTheproblem is thus to yavoid these high temperatures which are. used Yin'electric ovens Iforjcarrying outthe prior vprocesses and to em'V at vwhich with maximum silicon vapourization a maximum vapourization in the formof SiS and not in the form'fof SiS2 results.

It has, been fauna thatibetweenthse/tempera;

ture limits reaction between ZnS', A1203 and C proceeds very slowly infgthe direction of A1283 formation. Apart from the fact that thereby-.as

is avoidedalso afusion'o'f thecharge ,which can only .be caused b y the lower melting point of A1283 can be checked. Y'

.'.When thereis a detectable iron contant'apart from 'thel main 'impurities consisting of. s ilicic acid in the raw material it isto be noted that as a result 'of the extremeftendency of silica to form vapourous .SiS even in the Apresence of iron, no

ironfsiliconfalloy is obtained. Investigation'has.

shown that at the temperature in question 1o! v phere. V

about 1350o C. to 1.4000' C. no heedneed be paid to the formation of iron silicon alloys from siliciov acid and any, iron' oxide which maybe present.

From numerous experiments -in the present iield Vthree results may be given which were Vobtained under the same conditions.' A mixture of'v kaolin vanclbauxite containing silicio acid was heated tof/135090 for thirty minutes with Zinc blend and'carbongff'lhefollowing figures show that'theproportion of alumina to silicio acid is displaced completely in the direction of alumina.

The process is' thus vto be carried'outin the following manner: l I Q v'I he raw material lto be freed fromsilicic acid namelyy oxidesv of f aluminium, beryllium, mag' 1 nesium, zirconium, chromium, vanadium and so on are thoroughly mixed in finely' dividedV f orm with zinc blend andfcarbon', and in such proportions thatvfor 60 parts offsilicic acid inthe mix.-

ture there arelOQ parts'of ZnS and about vparts of carbon.`, In this connection it V is ummportant WhetherY the mixture so `obtained y'is heated in lpowder' form, Vbriquetted or otherwise pressed o'r'sintered. The heating i'sr'eieotedin such manner thaty the material is brought 'as rapidly as possible'to the temperature of 11350 to 1400D C.'requisi te for therapid volatili'za'tiono silicon inthe V`form of SiS., Above all the tem-'- perature'range of from 900 tou1100 C. must be rapidly traversed in order to avoid premature loss of sulphur 'asZrr-C-SgH If the heating takes place' in' ovens whichv do not permit avoidance Ab1! Acontact"with combustible, gases containingpo'ssibly an excess of air, an excess of carbon is em-v ployed to ensure a,i .reduc ng orneutral' atmoscon, carbon and' sulphur the gases liberated 'from ther oven, have a, high? combustibility. They are burnt to`pro.duce z`incoxide andsilicic acid, from whichthe former, maybe' removed by lixiviation with vacidsjor falkalics as" an electrolyte of conL `siderable parity. According to the temperature atwhich the burning action isallow'ecl to takev placel there are. obtained as 'byproductsy either an'ins'oluble' s ili'cicacid or acolloidal silicicwhich maybe' vconverted into vsilica gel. 'I he advanl tages fof this process reside injthat bya single processa completebreakingdown of the initial siliciov acid-containing raw materia1 i's Veffected without complex'byproductsv together with 'a simultaneous blend oxidationprocess whichmust otherv Jise be undertakenf separately in -j order Vto obtain Zinc. Y Thus a zinc mine vis in Vthe position if its prep' aration plan 'producesv in addition to blend, a1.

uminous wastegangue, to prepare therefrom in one operation pure alumina, silicio/acid gel and zinc liquor. Also vbauxite very rich'f in'V 'silicio acid can be treated `from the standpoint oflaluminarecoverywhile the zinc sulphide expendi- .l f

ture` remains within economic boundaries, par-y ticularlyasit hasbeen found possible to reduce by flotation .thesilicic acidcontent to .about S1-'12% of- Si02. vIncases where this possibility is `.presentthe lowest possible silicio acid content is reached by flotation and the remainder' voltatilized with the aid of-zinc sulphide. Since also tained by wet mechanical treatment must be re,- duced to the nest divided state. j

In order to render the explanation of the preceding methodv clearer all that has been discussed l containing silicio acid. and aluminum oxide and is exclusively the vapourization of the silicon with the aid of zinc sulphide. It is also possible, however, to bring about the conversion of silicon to 'SiS with other metal sulphides withvthe exception of A1283 and for this purpose even FeS` may be employed. In contradistinction to the, processes hitherto known and described it is necessary to keep the temperatures low about 1350 to 1400 C'. in order to avoid as far as'possible `the formation of AlzSa and the vapourization of SiSz,

1. A process for the treatment of materials containing at least oneof thelmaterials silicic'acid andl silicates; and oxides of metals; comprising,V rapidly heating the materials in mixture with zinc sulphide and carboniferous substances toa Vsi'ntering temperature of about 1350 1450 C., removing thesilicic acid as s'ilicon-subsulphide, and 1 recovering the metal-'oxides from the residue. 2. A process for the treatment 'of materials oxides of other metals, consistinginrapidly heat` g i. ing` these materials in mixture with zinc sulphide and `carboniferc'ius substances to asintering temf perture of aboutv 113501450b` 5C., removing lthe silicicacid as si1icon.SubSuIphide,` and recoveringv the'aluminum-oxide from thelresidue in any appropriate manner. j 1 .XAVERSIEBERS r L Q ERNST JUSTUS KOHLMEYER. i 

